package class03;

/**
 * @author zhangchaoliang
 * create 2022
 */
public class MergeSort5 {
    public static void mergeSort1(int[] arr) {
        if (arr == null || arr.length < 2)
            return;
        process(arr, 0, arr.length - 1);
    }

    public static void process(int[] arr, int L, int R) {
        if (L == R)
            return;
        int mid = L + ((R - L) >> 1);
        process(arr, L, mid);
        process(arr, mid + 1, R);
        merge(arr, L, mid, R);
    }

    public static void merge(int[] arr, int L, int M, int R) {
        int[] help = new int[R - L + 1];
        int i = 0;
        int p1 = L;
        int p2 = M + 1;
        while (p1 <= M && p2 <= R)
            help[i++] = arr[p1] <= arr[p2] ? arr[p1++] : arr[p2++];
        while (p1 <= M)
            help[i++] = arr[p1++];
        while (p2 <= R)
            help[i++] = arr[p2++];
        for (i = 0; i < help.length; i++)
            arr[L + i] = help[i];

    }

    public static void mergeSort2(int[] arr) {
        if (arr == null || arr.length < 2)
            return;
        int N = arr.length;
        int mergeSize = 1;
        while (mergeSize < N) {
            int L = 0;
            while (L < N) {
                int M = L + mergeSize - 1;
                if (M >= N)
                    break;
                int R = Math.min(M + mergeSize, N - 1);
                merge(arr, L, M, R);
                L = R + 1;
            }
            if (mergeSize > N / 2)
                break;
            mergeSize <<= 1;
        }

    }

    public static int[] generateRandomArray(int maxSize ,int maxValue){
        int[] arr = new int[(int)((maxSize+1)*Math.random())];
        for (int i=0;i<arr.length;i++)
            arr[i]=(int)((maxValue+1)*Math.random())-(int) ((maxValue+1)*Math.random());
        return arr;
    }

    public static int[] copyArray(int[] arr){
        if (arr==null)
            return null;
        int[] res = new int[arr.length];
        for (int i =0;i<arr.length;i++)
            res[i]=arr[i];
        return res;
    }

    public static boolean isEqual(int[] arr1,int[] arr2){
        if ((arr1!=null&&arr2==null)||(arr1==null&&arr2!=null))
            return false;
        if (arr1==null&&arr2==null)
            return true;
        if (arr1.length!=arr2.length)
            return false;
        for (int i=0;i<arr1.length;i++){
            if (arr1[i]!=arr2[i])
                return false;
        }
        return true;
    }

    public static void printArray(int[] arr){
        if (arr==null)
            return;
        for (int i =0;i<arr.length;i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }

    public static void main(String[] args) {
        int testTime = 500000;
        int maxSize = 100;
        int maxValue = 100;
        System.out.println("test begin!");
        for (int i=0;i<testTime;i++){
            int[] arr1 = generateRandomArray(maxSize,maxValue);
            int[] arr2 = copyArray(arr1);
            mergeSort1(arr1);
            mergeSort2(arr2);
            if (!isEqual(arr1,arr2)){
                System.out.println("Oops!");
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println("test end!");
    }
}
